The conventional screwdriver has a handle and a shank which is fixed to the handle. The output torque is not adjusted. However, for some objects, the torque that is applied to the object is set within a specific range and the threads of the object can be broken if the torque is exceeded over the pre-set range. A torque adjustable screwdriver is disclosed in Taiwan Utility Model No. M306166 and comprises a handle, a torque member, a transmission device, a stop and a cap. The torque member has a resilient member and a slide wherein the resilient member is located in the space of the handle and the slide has grooves with which the ridges of the handle are engaged, so that the slide is movable along the ridges of the handle and stopped by the stop. The transmission device has a transmission member and a driving rod which is connected to the transmission member. The driving rod has a driving end which extends through the hole of the slide, the torque member and the hole in the handle. The transmission member has a face which is located corresponding to the guide face of the slide. The driving rod and the transmission member each has a positioning portion at the tow respective facing ends. The output torque is adjusted when the cap is rotated. However, the adjustment cannot be observed by the user when adjusting the torque, so that the user has to set the times of revolutions of the cap each time of use. This is inconvenient and has low efficiency. The torque cannot be micro-adjusted. Besides, when using the screwdriver, shaking may be transferred to the parts in the screwdriver and the parts can be loosened, such that the torque cannot be set precisely.
The present invention intends to provide a torque adjustment device for a screwdriver and the torque adjustment device is micro-adjustable and the parts of the device are well positioned to improve the shortcomings mentioned above.